Time division duplex (tdd) uplink downlink (ul-dl) reconfiguration

ABSTRACT

Technology for performing a Time Division Duplex (TDD) uplink-downlink (UL-DL) reconfiguration in a heterogeneous network (HetNet) is described. An evolved node B (eNB) may identify cluster metrics for a plurality of evolved node Bs (eNBs) in a cell cluster of the HetNet. The plurality of eNBs in the cell cluster may have a backhaul latency within a selected range. The eNB may select a TDD UL-DL configuration index for the plurality of eNBs in the cell cluster based in part on the cluster metrics. The eNB may transmit the TDD UL-DL configuration index to one or more user equipments (UEs) located within the cell cluster using a downlink control information (DCI) format. The TDD UL-DL configuration index may be transmitted on a Common Search Space (CSS) of a physical downlink control channel (PDCCH) on a UE-specific Primary Cell (PCell).

RELATED APPLICATIONS

The present application claims priority to U.S. Provisional PatentApplication No. 61/841,230, filed Jun. 28, 2013 with a docket number ofP57460Z, the entire specification of which is hereby incorporated byreference in its entirety for all purposes.

BACKGROUND

Wireless mobile communication technology uses various standards andprotocols to transmit data between a node (e.g., a transmission stationor a transceiver node) and a wireless device (e.g., a mobile device).Some wireless devices communicate using orthogonal frequency-divisionmultiple access (OFDMA) in a downlink (DL) transmission and singlecarrier frequency division multiple access (SC-FDMA) in an uplink (UL)transmission. Standards and protocols that use orthogonalfrequency-division multiplexing (OFDM) for signal transmission includethe third generation partnership project (3GPP) long term evolution(LTE), the Institute of Electrical and Electronics Engineers (IEEE)802.16 standard (e.g., 802.16e, 802.16m), which is commonly known toindustry groups as WiMAX (Worldwide interoperability for MicrowaveAccess), and the IEEE 802.11 standard, which is commonly known toindustry groups as WiFi.

In 3GPP radio access network (RAN) LTE systems, the node can be acombination of Evolved Universal Terrestrial Radio Access Network(E-UTRAN) Node Bs (also commonly denoted as evolved Node Bs, enhancedNode Bs, eNodeBs, or eNBs) and Radio Network Controllers (RNCs), whichcommunicate with the wireless device, known as a user equipment (UE).The downlink (DL) transmission can be a communication from the node(e.g., eNodeB) to the wireless device (e.g., UE), and the uplink (UL)transmission can be a communication from the wireless device to thenode.

In homogeneous networks, the node, also called a macro node, can providebasic wireless coverage to wireless devices in a cell. The cell can bethe area in which the wireless devices are operable to communicate withthe macro node. Heterogeneous networks (HetNets) can be used to handlethe increased traffic loads on the macro nodes due to increased usageand functionality of wireless devices. HetNets can include a layer ofplanned high power macro nodes (or macro-eNBs) overlaid with layers oflower power nodes (small-eNBs, micro-eNBs, pico-eNBs, femto-eNBs, orhome eNBs [HeNBs]) that can be deployed in a less well planned or evenentirely uncoordinated manner within the coverage area (cell) of a macronode. The lower power nodes (LPNs) can generally be referred to as “lowpower nodes”, small nodes, or small cells.

The macro node can be used for basic coverage. The low power nodes canbe used to fill coverage holes, to improve capacity in hot-zones or atthe boundaries between the macro nodes' coverage areas, and improveindoor coverage where building structures impede signal transmission.Inter-cell interference coordination (ICIC) or enhanced ICIC (eICIC) maybe used for resource coordination to reduce interference between thenodes, such as macro nodes and low power nodes in a HetNet.

Homogeneous networks or HetNets can use time-division duplexing (TDD)for DL or UL transmissions. Time-division duplexing (TDD) is anapplication of time-division multiplexing (TDM) to separate downlink anduplink signals. In TDD, downlink signals and uplink signals may becarried on a same carrier frequency where the downlink signals use adifferent time interval from the uplink signals, so the downlink signalsand the uplink signals do not generate interference for each other. TDMis a type of digital multiplexing in which two or more bit streams orsignals, such as a downlink or uplink, are transferred apparentlysimultaneously as sub-channels in one communication channel, but arephysically transmitted on different resources.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of the disclosure will be apparent from thedetailed description which follows, taken in conjunction with theaccompanying drawings, which together illustrate, by way of example,features of the disclosure; and, wherein:

FIG. 1 illustrates a diagram of dynamic uplink-downlink (UL-DL)reconfiguration usage in a time-division duplexing (TDD) system inaccordance with an example;

FIGS. 2A-2C illustrate a time-division duplexing (TDD) system withvarious traffic adaptation time scales in accordance with an example;

FIG. 3 illustrates uplink downlink (UL-DL) interference due tonon-aligned UL-DL reconfiguration switching points in accordance with anexample;

FIG. 4 is a table of downlink control information (DCI) format Xperiodicity and subframe offset configurations in accordance with anexample;

FIG. 5A illustrates an abstract syntax notation (ASN) code example of adownlink control information (DCI) format X configuration in accordancewith an example;

FIG. 5B is a table of downlink control channel (DCI) configuration indexfield descriptions in accordance with an example;

FIG. 6 illustrates a block diagram of a coordinated multipoint (COMP)system in a heterogeneous network with low power nodes in accordancewith an example;

FIG. 7A illustrates a downlink control channel (DCI) format Xtransmission in a coordinated multipoint (COMP) scenario 4 in accordancewith an example;

FIG. 7B illustrates a radio frame with downlink control channel (DCI)format X subframes for a DCI format X transmission in a coordinatedmultipoint (COMP) scenario 4 in accordance with an example;

FIG. 8 illustrates a radio frame with downlink control channel (DCI)format X subframes having a repeated transmission pattern for a DCIformat X transmission in a coordinated multipoint (COMP) scenario 4 inaccordance with an example;

FIG. 9 depicts functionality of computer circuitry of an evolved node B(eNB) operable to perform a Time Division Duplex (TDD) uplink-downlink(UL-DL) reconfiguration in a heterogeneous network (HetNet) inaccordance with an example;

FIG. 10 depicts functionality of computer circuitry of a user equipment(UE) operable to implement a Time Division Duplex (TDD) uplink-downlink(UL-DL) reconfiguration in a heterogeneous network (HetNet) inaccordance with an example;

FIG. 11 depicts a flow chart of a method for performing a Time DivisionDuplex (TDD) uplink-downlink (UL-DL) reconfiguration in a heterogeneousnetwork (HetNet) in accordance with an example; and

FIG. 12 illustrates a diagram of a wireless device (e.g., UE) inaccordance with an example.

Reference will now be made to the exemplary embodiments illustrated, andspecific language will be used herein to describe the same. It willnevertheless be understood that no limitation of the scope of theinvention is thereby intended.

DETAILED DESCRIPTION

Before the present invention is disclosed and described, it is to beunderstood that this invention is not limited to the particularstructures, process steps, or materials disclosed herein, but isextended to equivalents thereof as would be recognized by thoseordinarily skilled in the relevant arts. It should also be understoodthat terminology employed herein is used for the purpose of describingparticular examples only and is not intended to be limiting. The samereference numerals in different drawings represent the same element.Numbers provided in flow charts and processes are provided for clarityin illustrating steps and operations and do not necessarily indicate aparticular order or sequence.

EXAMPLE EMBODIMENTS

An initial overview of technology embodiments is provided below and thenspecific technology embodiments are described in further detail later.This initial summary is intended to aid readers in understanding thetechnology more quickly but is not intended to identify key features oressential features of the technology nor is it intended to limit thescope of the claimed subject matter.

A dynamic Time Division Duplex (TDD) uplink-downlink (UL-DL)reconfiguration scheme for heterogeneous networks (HetNets) is describedherein. A plurality of evolved node Bs (eNBs) in a cell cluster mayexchange inter-eNB messages over an X2 interface. The eNBs in the cellcluster may have a backhaul latency within a selected range. Theinter-eNB messages may contain cluster metrics associated with the eNBs,wherein the cluster metrics may include UL-DL configurations being usedby eNBs within the cell cluster, DL-UL resources required by each eNB,and/or buffer sizes in UL and DL transmission direction and packetdelays. An eNB in the cell cluster may select a TDD UL-DL configurationindex for the plurality of eNBs in the cell cluster using the clustermetrics. In other words, the eNB may use the inter-eNB messages, and thecluster metrics within the inter-eNB messages, to negotiate a unifiedUL-DL configuration in a distributed manner for multiple cells within acell cluster.

The eNB may transmit the TDD UL-DL configuration index to at least oneuser equipment (UE) located within the cell cluster. The eNB maytransmit the TDD UL-DL configuration index using a downlink controlinformation (DCI) format (i.e., referred to as DCI format X herein),wherein the TDD UL-DL configuration index is transmitted on a CommonSearch Space (CSS) of a physical downlink control channel (PDCCH) on aUE-specific Primary Cell (PCell). In addition, the eNB may inform theUE, via a Uu interface, of reconfiguration DCI monitoring subframesusing one of a bitmap technique or according to a DCI format Xperiodicity and subframe offset configuration. As a result, the UEconfigured with UL-DL reconfiguration may monitor the DCI format X in asmaller subset of configured DL subframes per duty cycle, therebyproviding a significant reduction in power consumption at the UE. Inaddition, supporting different UL/DL configurations for each individualTransmission Point (TP) in CoMP scenario 4 may be required wheninstantaneous UL/DL ratio is not correlated within each TP's cell.Therefore, DCI format X monitoring subframes for a plurality of TPs inCoMP scenario 4 may be time multiplexed onto different subframes toindicate independent UL/DL configuration in use.

Heterogeneous network (HetNet) deployments can offer efficient means toincrease cellular coverage and capacity compared to traditionalhomogeneous networks and may involve the co-existence of different radioaccess technologies (RAT), transmission-reception techniques, and basestation (BS) or node transmission powers amongst other possiblearchitectural combinations. The RAT can include the standard used, suchas LTE or IEEE 802.16, or the version of the standard, such as LTEversion 11, 3GPP LTE V11.0.0, IEEE 802.16n, or IEEE 802.16p. In anexample, the radio access technology (RAT) standard can include LTErelease 8, 9, 10, 11, or subsequent release. The transmission-receptiontechnique can include various transmission techniques, such as adownlink (DL) coordinated multi-point (CoMP) transmission, enhancedinter-cell interference coordination (eICIC), and combinations thereof.A node transmission power can refer to the power generated by a nodetype, such as a macro node (e.g., macro evolved Node B (eNB)) in a macrocell and multiple low power nodes (LPNs or small eNBs) in the respectivesmall cells, as illustrated in FIG. 1.

LTE TDD systems may operate synchronously in order to avoid strong DL-ULinter-cell interference between base stations (eNBs) and/or mobileterminals (UEs). The synchronous operation may imply that all cells in anetwork area use the same UL-DL configuration, wherein the UL-DLconfiguration may represent a frame configuration and can define anamount of DL and UL resources and is associated with an exclusive UL/DLratio in a radio frame. In addition, frame transmission boundaries maybe aligned in time.

Although synchronous operation may be effective from an interferencemitigation perspective, synchronous operation may not be optimal interms of traffic adaptation and may significantly degrade the perceivedpacket throughput in small cells. In addition, using the same frameconfiguration in HetNet deployments, with many low power nodesdistributed over a typical macro cell area, may be inefficient from auser experience perspective. The traffic in HetNet deployments maysignificantly vary over time or cell domains. At a given time instance,a particular set of cells may have dominant traffic in one transmissiondirection (i.e., either DL or UL), so that additional spectrum resourcesare required in the dominant traffic direction. In HetNet deployments, alevel of isolation between eNBs may be higher as compared to a macrocell environment because of the proximity of the small cells to the endusers. As a result, a relatively large portion of the eNBs may beconsidered as isolated cells. These isolated cells may modify an UL-DLconfiguration in order to adapt to the instantaneous traffic conditions.On the other hand, small cells located relatively close to each othermay experience strong coupling on eNB links. The strong coupling mayresult in DL transmissions in one cell causing interference to the ULreception in neighboring cells.

Cell-clustering may be an effective solution for resolving DL-ULinterference mitigation in small cells. In cell clustering, a set ofcoupled cells may be combined into a cell cluster and joint trafficadaptation may be performed among the small cells. Cell clustering maybe efficient when coupled cells are served by the same eNB so thatinformation about traffic conditions from all cells is available to aneNB scheduler. The eNB scheduler may determine an optimal frameconfiguration on a relatively fast timescale. However, the coupled smallcells may not be controlled by the same eNB. When the coupled smallcells are not controlled by the same eNB, coordinating schedulingdecisions among cells may become difficult because a centralizedsolution for the coupled small cells may be unavailable. Dynamic trafficadaptation may be performed by selecting the same UL-DL configuration ifan adaptation time-scale (e.g., an UL-DL reconfiguration period of 10milliseconds (ms) is smaller than a backhaul latency (e.g., 40 ms-160ms), as discussed in further detail in 3GPP Technical Report (TR) TR36.932. In this case, the dynamic UL-DL reconfiguration may cause strongDL-UL interference at the subframes having opposite transmissiondirections in neighboring cells.

The backhaul latency may complicate decision making on a frameconfiguration between coupled eNBs. The backhaul latency may alsocomplicate control of the DL-UL interference if there is no coordinationamong cells. Although the DL-UL interference mitigation issue may beresolved by prohibiting traffic adaptation when coupled cells areconnected with a backhaul latency exceeding a 10 ms traffic adaptationtime scale, such an approach may be inefficient from a trafficadaptation perspective. As described in greater detail herein, the UL-DLreconfiguration time scale may be adjusted to the backhaul latencycharacteristics. In this case, cell-clustering may be applied at a lowertime scale and the network may avoid situations where one of the cellsbecomes an aggressor in terms of DL-UL interference, thereby causingdegradation to an UL performance experience.

A number of signaling options have been discussed for enhancedInterference Mitigation and Traffic Adaptation (eIMTA), including systeminformation block (SIB), paging, radio resource control (RRC), mediaaccess control (MAC) signaling, L1 signaling, and characteristics ofdifferent traffic adaptation time scales. The signaling of the UL/DLreconfiguration may use explicit L1 signaling of reconfiguration byUE-group-common Enhanced Physical Downlink Control Channel (ePDCCH) orPhysical Downlink Control Channel (PDCCH), referred to as (e)PDCCHherein, due to lower control overhead. The UE-group-common (e)PDCCH mayrefer to enhanced Control Channel Elements (eCCEs) or Control ChannelElement (CCE) commonly monitored by groups of UEs for controlinformation. When the (e)PDCCH is used, downlink control information(DCI) carriers by UE-group-common (e)PDCCH may be referred to as commonDCI herein.

However, using explicit L1 signaling of reconfiguration byUE-group-common (e)PDCCH may result in several potential problems.Higher power consumption may be expected due to additionalblind-detection attempts performed on UE-group-common (e)PDCCH when theUE does not know the existence of common DCI and the size of common DCIis different as compared with existing DCIs. Some mechanisms may berequired to be developed to further optimize the power consumption atthe UE side and improve the network capability to flexibly configure theUL/DL configuration via common DCI transmission subframes according tothe cell its own instantaneous cell-specific traffic, etc.

In addition, using the explicit L1 signaling may not support coordinatedmultipoint (CoMP) scenario 4. In CoMP scenario 4, all transmissionpoints (e.g., macro nodes, pico nodes, remote radio heads, and low powernodes) within the coverage area of the macro point may share the samephysical cell identifier (Cell-ID). It may be desirable to supportindependent UL/DL configurations for transmission points (TPs) atdifferent geographical locations in order to maximize throughputperformance since an instantaneous traffic status may be different indifferent TP coverage.

A dynamic UL-DL reconfiguration is described herein with configurableand synchronized configuration of duty cycles and subframe offsets. TheUL-DL reconfiguration may be used in a variety of practical scenarioswith different backhaul characteristics. In addition, the UL-DLreconfiguration may reduce a power consumption level at the UE andenable independent UL/DL reconfigurations for different RRHs in CoMPscenario 4. Therefore, the proposed UL-DL reconfiguration schemeachieves a power-efficient UL/DL reconfiguration indication and CoMPscenario 4 support for dynamic TDD UL/DL reconfiguration.

FIG. 1 illustrates a layered HetNet deployment with different nodetransmission powers using time-division duplexing (TDD). As used herein,a cell can refer to the node or the coverage area of the node. A lowpower node (LPN) can refer to a small node, which can include a smalleNB, a micro eNB, a pico node, a pico eNB, a femto-eNB, a home eNB(HeNB), a remote radio head (RRH), a remote radio equipment (RRE), or aremote radio unit (RRU). As used herein, the term “small node” may beused interchangeably with the term “pico node” (or pico eNB), and theterm “small cell” may be used interchangeably with the term “pico cell”in the examples to assist in distinguishing between the macro node andthe LPN or the small node, and the macro cell and the small cell. Themacro node can be connected to each LPN via backhaul link using X2interface or optical fiber connections.

The macro nodes can transmit at high power level, for example,approximately 5 watts (W) to 40 W, to cover the macro cell. The HetNetcan be overlaid with low power nodes (LPNs), which may transmit atsubstantially lower power levels, such as approximately 100 milliwatts(mW) to 2 W. In an example, an available transmission power of the macronode may be at least ten times an available transmission power of thelow power node. A LPN can be used in hot spots or hot-zones, referringto areas with a high wireless traffic load or high volume of activelytransmitting wireless devices (e.g., user equipments (UEs)). A LPN canbe used in a microcell, a picocell, a femtocell, and/or home network.Femto_Cell0 illustrates downlink traffic heavy usage by the wirelessdevices (e.g., UEs) and Femto_Cell1 illustrates uplink traffic heavyusage by the wireless devices.

Allowing adaptive UL-DL configurations depending on traffic conditionsin different cells can significantly improve the system performance insome examples. FIG. 1 illustrates an example where different UL-DLconfigurations can be considered in different cells. Networks (e.g.,HetNets or homogeneous networks) can involve a same carrier or differentcarriers deployed by a single operator or different operators in thesame band and employing either a same or different uplink-downlink(UL-DL) configurations. Where possible, interference may includeadjacent channel interference (when different carrier frequencies areused) as well as co-channel interference (when a same carrier frequencyis used) such as remote node-to-node interference (or BS-to-BSinterference or eNB-to-eNB interference).

Legacy LTE TDD can support asymmetric UL-DL allocations by providingseven different semi-statically configured uplink-downlinkconfigurations. Table 1 illustrates seven UL-DL configurations used inLTE, where “D” represents a downlink subframe, “S” represents a specialsubframe, and “U” represents an uplink subframe. In an example, thespecial subframe can operate or be treated as a “truncated” downlinksubframe.

TABLE 1 Uplink-downlink Subframe number configuration 0 1 2 3 4 5 6 7 89 0 D S U U U D S U U U 1 D S U U D D S U U D 2 D S U D D D S U D D 3 DS U U U D D D D D 4 D S U U D D D D D D 5 D S U D D D D D D D 6 D S U UU D S U U D

As illustrated by Table 1, UL-DL configuration 0 can include 6 uplinksubframes in subframes 2, 3, 4, 7, 8, and 9, and 4 downlink and specialsubframes in subframes 0, 1, 5, and 6; and UL-DL configuration 5 caninclude one uplink subframe in subframe 2, and 9 downlink and specialsubframes in subframes 0, 1, and 3-9.

As an underlying requirement in some examples, all cells of the networkchange UL-DL (TDD) configurations synchronously in order to avoid theinterference. However, such a requirement can constrain the trafficmanagement capabilities in different cells of the network. The legacyLTE TDD set of configurations can provide DL subframe allocations in therange between 40% and 90%, as shown in Table 1. The UL and DL subframesallocation within a radio frame can be reconfigured through systeminformation broadcast signaling (e.g., system information block [SIB]).Hence, the UL-DL allocation once configured can be expected to bechanged semi-statically.

Predetermined or semi-statically configured UL-DL configurations may notmatch the instantaneous traffic situation which can result ininefficient resource utilization, especially in cells with a smallnumber of users that download or upload large amounts of data. AdaptiveUL-DL configurations can be used to handle cell-dependent trafficasymmetry and match instantaneous traffic situations but can generatedifferent types of interferences if not taken into consideration. Forsuch time division LTE (TD-LTE) deployments with different UL-DLconfigurations in different cells, the new types of interferences due toasymmetric UL-DL configurations can include node-to-node (or BS-to-BS)and UE-to-UE interference, which can be mitigated using variousmechanisms described herein. The impact of the inter-cell UL-DL(node-to-node) interference can significantly reduce the benefitsobtained from the adaptability of UL-DL configurations in differentcells.

As described herein, a dynamic uplink-downlink (UL-DL) reconfigurationscheme may include configurable and synchronized duty cycles, so thatthe dynamic UL-DL reconfiguration may be used in a variety of practicalscenarios with different backhaul characteristics.

FIGS. 2A-2C illustrates exemplary time-division duplexing (TDD) systemswith various traffic adaptation time scales. FIG. 2A illustrates anisolated cell with a 10 millisecond (ms) adaptation time scale. FIG. 2Aillustrates a downlink or uplink (DL/UL) signal transmission on servinglinks between a UE and an eNB. FIG. 2B illustrates as isolated cellcluster with a 40 ms traffic adaptation time scale. FIG. 2B illustrateseNB-eNB propagation links with a low path loss between a first eNB and asecond eNB. In addition, FIG. 2B illustrates a DL or UL inter-cellinterference between a UE and an eNB. FIG. 2C illustrates an isolatedcell cluster with an 80 ms traffic adaptation time scale. FIG. 2Cillustrates eNB-eNB propagation links with a low path loss between afirst eNB and a second eNB. In addition, FIG. 2C illustrates a DL or ULinter-cell interference between a UE and an eNB.

Backhaul latency characteristics may be generally known to networkoperators. The one-way backhaul latency in operator-controlled networksmay be in a range from 5 ms (e.g., Fiber Access 1) to 60 ms (e.g., DSLtechnology). Therefore, different UL-DL reconfiguration periods may beassumed for isolated cells and coupled cells combined into one cluster(e.g., two coupled cells). For instance, a period of 10 ms, 40 ms, 80ms, or 160 ms may be assumed for different types of backhaul links thatconnect coupled eNBs. Therefore, multiple reconfiguration periods may besupported. As a result, the isolated cells may be configured with the 10ms adaptation time scale, and the cells clusters formed from coupledcells may be configured with a lower/higher adaptation time scale. Thetraffic adaptation time scale in the clusters may depend on multiplefactors, including a number of cells in the cell cluster and backhaullatency characteristics.

Therefore, the TDD UL-DL configuration index for the plurality of eNBsin the cell cluster may be selected according to a defined periodicity,wherein the defined periodicity is based on the backhaul latency of theplurality of eNBs in the cell cluster and includes 10 milliseconds (ms),20 ms, 40 ms and 80 ms. Information about the UL-DL reconfigurationperiod may be communicated to the cells over an X2 interface andpre-configured by the network operator.

FIG. 3 illustrates uplink downlink (UL-DL) interference due tonon-aligned UL-DL reconfiguration switching points. In addition todetermining the UL-DL reconfiguration period when using cell-clusteringbased techniques for DL-UL interference mitigation, UL-DLreconfigurations may be performed synchronously in order to avoid DL-ULinterference. In other words, the UL-DL reconfigurations may beperformed at the same frame instances in time. As shown in FIG. 3,having different switching points at coupled eNBs may result in DL-ULinterference. Therefore, in order to synchronize the UL-DLreconfiguration switching points, a system frame number (SFN) countermay be used so that each cell updates its UL-DL configurationsynchronously in time. In other words, UL-DL the reconfiguration periodsmay be aligned in time in order to avoid DL-UL interference. The SFNcounter may be used to control a radio frame having a SFN modperiodicity of zero, wherein a TDD UL-DL configuration index is appliedby eNBs in the cell cluster so that the TDD UL-DL configuration issynchronously updated by eNBs within the cell cluster.

In order to perform the same distributed decisions on the actual UL-DLconfiguration to be applied over the air, a distributed protocol may beused. The cells may exchange information about traffic conditions foreach transmission direction among coupled cells in cluster. In otherwords, a TDD UL-DL configuration index for the plurality of eNBs in thecell cluster may be selected based on cluster metrics, wherein thecluster metrics are exchanged between the plurality of eNBs in the cellcluster over an X2 interface. As an example, a cell cluster may includea first eNB, a second eNB and a third eNB. The first eNB may sendcluster metrics associated with the first eNB to the second eNB and thethird eNB. Similarly, the first eNB may receive cluster metrics from thesecond eNB and the third eNB.

Examples of cluster metrics exchanged between the eNBs may include theDL and UL buffer status combined with the DL and UL packet throughputs.In addition, the cells may exchange information regarding the preferredUL-DL configuration for the next reconfiguration cycle. This informationmay be considered as the rough quantized measure of the DL and ULtraffic demands.

The LTE legacy set of UL-DL configuration supports the followingproportion between DL and UL subframes: 4:6, 5:5, 6:4, 7:3, 8:2, 9:1.This set may be extended to cover the whole set of possible proportionsby adding 0:10, 1:9, 2:8, 3:7, 4:6, 10:0. If the preferred UL-DLconfigurations are exchanged over the X2 interface, then cells may applyone of the predefined strategies to perform traffic adaptation. Forinstance, each cell may select the UL-DL configuration with a minimumnumber of DL subframes among all received UL-DL configurations.Alternatively, cells may select DL/UL balanced configuration byselecting the average number of DL subframes that can be applied in allcells.

In order to force coupled eNBs to choose the same TDD configuration, thefollowing distributed decision at each eNB can be made:tddConfigIndex=decisionFunction (M1, M2, . . . , MN), whereintddConfigIndex is a chosen UL-DL configuration index, Mi are clustermetrics exchanged between eNBs in a cell cluster, and decisionFunctionis an algorithm to decide about the new UL-DL configuration. Since theeNBs may receive equal sets of cluster metrics, the above algorithm cancalculate equal TDD configuration indexes for the eNBs in a cellcluster, and thus align transmission directions.

In some examples, the cluster metrics exchanged between eNBs in the cellcluster may include, but is not limited to, UL-DL configurations, arelative amount of required DL/UL resources, buffer sizes in UL and DL,and packet delays. In addition, the decision function described abovemay choose the TDD configuration which corresponds to a mean of thereported cluster metrics or the chosen TDD configuration may correspondto a maximum (or minimum) of the reported cluster metrics.

Signaling may be provided to UE terminals in order to support dynamicUL-DL reconfiguration with a configurable time scale. In other words,the signaling may be for power-efficient TDD UL-DL reconfigurationindication. The eNB may transmit the TDD UL-DL configuration index toone or more UEs located within the cell cluster. The signaling may beconsidered independently from the DL-UL interference mitigation schemedescribed above (i.e. cell-clustering) and applied in order to reduce UEpower consumption, decrease system overhead, improve link adaptation,increase reception reliability and provide long-term traffic adaptationdecisions.

In order to support the UL/DL reconfiguration, a new downlink controlinformation (DCI) format, called as DCI format X herein, may be used forthe UL/DL reconfiguration indication. The DCI format X may be the DCIformat of its corresponding common DCI used for the UL/DLreconfiguration indication. The TDD UL-DL configuration index may betransmitted on a UE-group-common Enhanced Physical Downlink ControlChannel (EPDCCH) or Physical Downlink Control Channel (PDCCH).

The DCI format X transmission may include a configurable duty cycle andsubframe offset design. The configurable DCI format X transmissionsubframes may offer several advantages, such as the UE configured withUL-DL re-configuration may only monitor the DCI format X in smallersubset of configured DL subframe(s) per duty cycle, thereby providing asignificant reduction in power consumption. In addition, different DCIformat X may be required in order to support CoMP scenario 4 withdifferent UL/DL configurations. Therefore, as described in furtherdetail below, the DCI format X for different remote radio heads (RRHs)in CoMP scenario 4 may be configured to be time-multiplexed ontodifferent subframes to be used to indicate independent UL/DLconfigurations.

In order to reduce a false detection probability and avoid unnecessaryblind decoding attempts, DCI format X may be transmitted only insubframes which are used for downlink transmission in all legacy UL/DLconfigurations. In other words, DCI format X may be allowed to betransmitted on subframe #0, #1, #5 and #6 in each frame. The periodicityof DCI format X may be configurable and represented as a predefined setof possible configurations.

FIG. 4 is an exemplary table of downlink control information (DCI)format X periodicity and subframe offset configurations. The periodicityfor transmitting DCI format X, from an eNB in the cell cluster to theUE, may vary from 10 ms to 80 ms in a TDD system, as shown in FIG. 4. ADCI format X configuration I_(DCI) may range from 0 to 15. The DCIformat X configuration I_(DCI) may be represented in a binary format(e.g., 0000, 0101, and 1001). A configuration period T_(DCI) may rangefrom 10 subframes to 80 subframes. In addition, a transmission offsetmay range from 0 subframes to 3 subframes.

The eNB may inform the UE, via a Uu interface, of the reconfigurationDCI monitoring subframes using the exemplary table shown in FIG. 4 or abitmap technique. An X-bit bitmap may indicate a set of systeminformation block type 1 (SIB1) downlink or special (DL/S) subframes(SIB-1 DL/S subframes). Starting from a most significant bit (MSB) to aleast significant bit (LSB), the bitmap corresponds to subframe #{[Xa,Xb, Xc, . . . ]}. The bit “1” may indicate that the UE shall monitor thereconfiguration DCI in the corresponding subframe, and the bit “0” mayindicate that the UE shall not monitor the reconfiguration DCI in thecorresponding subframe.

The periodicity of the reconfiguration signals may include 10 ms, 20 ms,40 ms, or 80 ms. The UE may monitor the reconfiguration signals indownlink subframes or special subframes according to UL/DL configurationindicted in SIB1. The UE may be configured to monitor thereconfiguration signals in more than one subframe between two adjacentperiodic instances. The detected configuration may be valid for a windowwhere the window has a duration equal to the periodicity of thereconfiguration signals. The UE may assume the same configuration fortwo or more reconfiguration signals, if the two or more reconfigurationsignals are detected in subframes within a window of a duration equal tothe periodicity of the reconfiguration signals. In addition, the UE maynot assume the same configuration for reconfiguration signals detectedin subframes across different windows.

FIG. 5A illustrates an abstract syntax notation (ASN) code example of adownlink control information (DCI) format X configuration. FIG. 5B is atable of downlink control channel (DCI) configuration index fielddescriptions. A configuration of the DCI format X transmission may beindicated by the eNB through UE-Specific dedicated RRC signaling foreach serving cell independently using a 4-bit UE-Specific parameter. Asshown in FIG. 5A, the DCI configuration index may range from 0 to 15. Asshown in FIG. 5B, the DCI configuration index may include an I_(DCI)parameter, wherein I_(DCI) is defined for the DCI format X configurationthat is applied for the TDD system.

Since UL/DL reconfiguration is particularly beneficial for a typicalEnhanced Interference Mitigation & Traffic Adaptation (eIMTA) scenariowhere a limited number of UEs have traffic to be served, the signalingoverhead for the UL-DL reconfiguration indication may be minimal. Whenno configuration of DCI format X transmission is received, UE may followa fallback configuration that is either the UL/DL configurationindicated in the System Information Block 1 (SIB1) or a latest UL/DLconfiguration indicated by the DCI format X transmission.

FIG. 6 illustrates an example of a CoMP system with low power nodes(LPNs) in a macro cell coverage area. FIG. 6 can illustrate LTE CoMPscenarios 3 and 4. In the intra-site CoMP example illustrated in FIG. 6,LPNs (or RRHs) of a macro node 610A may be located at differentlocations in space, and CoMP coordination may be within a singlemacrocell. A coordination area 604 can include eNBs 610A and LPNs680N-S, where each LPN can be configured to communicate with the eNB viaa backhaul link 632 (optical or wired link). A cell 626A of a macro nodemay be further sub-divided into sub-cells 630N-S. LPNs (or RRHs) 680N-Smay transmit and receive signals for a sub-cell. A wireless device 602can be on a sub-cell edge (or cell-edge) and intra-site CoMPcoordination can occur between the LPNs (or RRHs) or between the eNB andthe LPNs. In CoMP scenario 3, the low power RRHs providingtransmission/reception points within the macrocell coverage area canhave different cell IDs from the macro cell. In CoMP scenario 4, the lowpower RRHs providing transmission/reception points within the macrocellcoverage area can have a same cell ID as the macro cell.

FIG. 7A illustrates a downlink control channel (DCI) format Xtransmission in a coordinated multipoint (COMP) scenario 4. DCI format Xtransmissions from low power remote radio heads (RRHs) with a same cellIDs within a macro-cell coverage may be time-domain multiplexed byassigning them to different subframe offsets together with same ordifferent duty cycles, depending on instantaneous traffic conditionsassociated with the RRHs. FIG. 7A illustrates setting the periodicityand subframe offset of DCI format X. Two RRHs, i.e., Transmission Point1 (TP1) and TP2, may be within a macro coordination area having the samecell-ID (e.g., Cell-ID 0). Upon receiving the UE capability of UL-DLreconfiguration support in Step 1, the network may indicate the DCIformat X subframe configuration in Step 2 for each UE according to itsgeographical location. In the example shown in FIG. 7A, the network maysend a dedicated RRC configuration with index 0 to a UE in proximity toTP0. In addition, the network may send a dedicated RRC configurationwith index 2 to a UE located in proximity to TP1. As a result, thenetwork may take advantage of flexible and independent UL-DLconfiguration for TP0 and TP1 separately depending on instantaneoustraffic conditions associated with TP0 and TP1.

As the DCI format X may be required to be received with high reliability(e.g., with DCI decoding error probability in the range of 1e-5 and1e-6), the DCI format X may be transmitted repeatedly within a fixedrepetition period (e.g. 5 ms or 10 ms). The repetition mechanism mayalso be used with a configurable DCI format X periodicity and offsetwith proper configuration selection at the network side.

FIG. 7B illustrates a radio frame with downlink control channel (DCI)format X subframes for a DCI format X transmission in a coordinatedmultipoint (COMP) scenario 4. As shown in FIG. 7B, the DCI format Xtransmission may include a DCI format X subframe for TP0 with aconfiguration index 0 in a first subframe of a radio frame. In addition,the DCI format X transmission may include a DCI format X subframe forTP1 with a configuration index 2 in a sixth subframe of a radio frame.

FIG. 8 illustrates a radio frame with downlink control channel (DCI)format X subframes having a repeated transmission pattern for a DCIformat X transmission in a coordinated multipoint (COMP) scenario 4. TheDCI format X may be transmitted twice per 5 ms. As an example, in orderto achieve an independent UL/DL configuration setting in TP0 and TP1,the network may appropriately select configuration index 0 and 2 for theDCI format X transmission. The corresponding DCI format X transmissionpatterns for TP0 and TP1 with a 5 ms repeated transmission design isshown in FIG. 8. The DCI format X transmission may include a DCI formatX subframe for TP0 with a configuration index 0 in subframes 1 and 2 ofa radio frame. In addition, the DCI format X transmission may include aDCI format X subframe for TP1 with a configuration index 2 in subframes6 and 7 of a radio frame.

In some examples, it may be difficult to enable a UL/DL reconfigurationthat is too frequent, such as faster than once per 40 ms due to backhaullatency. However, the eNB may configure the UE with a 10 ms duty cycleof common DCI transmission in a four-repeated DCI transmissions patternwithin 40 ms period. As a result, the DCI may be transmitted in eachradio frame in order to inform the UEs about actual UL-DLconfigurations, but UL-DL reconfiguration may not change more frequentlythan a pre-configured period, which can benefit UEs that are in sleepmode and wake up in the middle of the reconfiguration period.

Another example provides functionality 900 of computer circuitry of anevolved node B (eNB) operable to perform a Time Division Duplex (TDD)uplink-downlink (UL-DL) reconfiguration in a heterogeneous network(HetNet). The functionality may be implemented as a method or thefunctionality may be executed as instructions on a machine, where theinstructions are included on at least one computer readable medium orone non-transitory machine readable storage medium. The computercircuitry can be configured to identify cluster metrics for a pluralityof evolved node Bs (eNBs) in a cell cluster of the HetNet, wherein theplurality of eNBs in the cell cluster have a backhaul latency within aselected range, as in 910. The computer circuitry can be configured toselect a TDD UL-DL configuration index for the plurality of eNBs in thecell cluster based in part on the cluster metrics, as in block 920. Thecomputer circuitry can be further configured to transmit the TDD UL-DLconfiguration index to one or more user equipments (UEs) located withinthe cell cluster using a downlink control information (DCI) format,wherein the TDD UL-DL configuration index is transmitted on a CommonSearch Space (CSS) of a physical downlink control channel (PDCCH) on aUE-specific Primary Cell (PCell), as in block 930.

In one example, the computer circuitry can be further configured toconfigure downlink control information (DCI) monitoring subframes forthe one or more UEs in the cell cluster using radio resource control(RRC) signaling in a UE-specific manner. In one example, the clustermetrics are exchanged between the plurality of eNBs in the cell clusterover an X2 interface, the cluster metrics including one or more of UL-DLconfigurations being used by eNBs within the cell cluster, DL-ULresources required by each eNB, buffer sizes in UL and DL transmissiondirection and packet delays.

In one example, the computer circuitry can be further configured toselect the TDD UL-DL configuration index for the plurality of eNBs inthe cell cluster based on a minimum, mean or maximum of the clustermetrics exchanged between the plurality of eNBs in the cell cluster in adistributed manner. In addition, the computer circuitry can be furtherconfigured to select the TDD UL-DL configuration index for the pluralityof eNBs in the cell cluster according to a defined periodicity, whereinthe defined periodicity is based on the backhaul latency of theplurality of eNBs in the cell cluster and includes 10 milliseconds (ms),20 ms, 40 ms and 80 ms.

In one configuration, the computer circuitry can be further configuredto use a System Frame Number (SFN) counter to control a radio framehaving a SFN mod periodicity of zero, wherein the TDD UL-DLconfiguration index is applied by eNBs in the cell cluster so that theTDD UL-DL configuration is synchronously updated by eNBs within the cellcluster. In addition, the computer circuitry can be further configuredto transmit TDD UL-DL configuration index information to the one or moreUEs in the cell cluster via a Uu interface, the TDD UL-DL configurationindex information being transmitted on a physical downlink controlchannel (PDCCH) in one or more of subframe numbers 0, 1, 5 or 6 in eachradio frame depending on a UE-specific RRC configuration. Furthermore,the computer circuitry can be configured to transmit the TDD UL-DLconfiguration index to the one or more UEs in the cell cluster accordingto a predefined periodicity of 10 subframes to 80 subframes and apredefined offset value of 0 subframes to 3 subframes.

In one example, the computer circuitry can be further configured totransmit the TDD UL-DL configuration index to the one or more UEslocated in proximity to one or more transmission points (TPs) in acoordinated multi-point (COMP) scenario 4, wherein the TDD UL-DLconfiguration index is transmitted to the one or more UEs according totraffic conditions associated with the one or more TPs. In addition, thecomputer circuitry can be further configured to transmit the TDD UL-DLconfiguration index to the one or more UEs located in proximity to oneor more transmission points (TPs) in a coordinated multi-point (COMP)scenario 4, wherein the TDD UL-DL configuration index is transmitted tothe one or more UEs according to a DL subframes pattern used fordownlink channel information (DCI) repeated transmission monitoring.

In one configuration, the computer circuitry can be further configuredto transmit the TDD UL-DL configuration index to the one or more UEs inthe cell cluster according to an X-bit bitmap indicating a set of systeminformation block type 1 (SIB1) downlink or special (DL/S) subframes,wherein the one or more UEs monitor for a downlink channel information(DCI) transmission from the eNB according to the X-bit bitmap, wherein‘X’ represents a number of bits within a bitmap string in which each bitindicates a particular SIB1 DL/S subframes, wherein a bit “1” indicatesthat the UE shall monitor for a DCI reconfiguration in a correspondingsubframe and a bit “0” indicates that the UE shall not monitor for theDCI reconfiguration in the corresponding subframe.

Another example provides functionality 1000 of computer circuitry of auser equipment (UE) operable to implement a Time Division Duplex (TDD)uplink-downlink (UL-DL) reconfiguration in a heterogeneous network(HetNet). The functionality may be implemented as a method or thefunctionality may be executed as instructions on a machine, where theinstructions are included on at least one computer readable medium orone non-transitory machine readable storage medium. The computercircuitry can be configured to indicate a capability of supporting a TDDUL-DL reconfiguration functionality to an evolved node B (eNB) via UEcapability reporting, as in block 1010. The computer circuitry can beconfigured to receive a configuration to enable TDD UL-DLreconfiguration at the UE, as in block 1020. The computer circuitry canbe further configured to receive a TDD UL-DL reconfiguration signal fromthe eNB in a downlink control information (DCI) message, as in block1030. In addition, the computer circuitry can be configured to update aTDD UL-DL configuration of the UE based on the TDD UL-DL reconfigurationsignal transmitted on a physical downlink control channel (PDCCH) inpreconfigured downlink or special (DL/S) subframes by the eNB, as inblock 1040.

In one example, the configuration to enable the TDD UL-DLreconfiguration at the UE includes at least one of a UE-specificreconfiguration radio network temporary identifier (RNTI),reconfiguration DCI monitoring subframes configuration information andan indicator index. In addition, the computer circuitry can be furtherconfigured to receive the TDD UL-DL reconfiguration signal from the eNBaccording to a defined periodicity of 10 milliseconds (ms), 20 ms, 40 msor 80 ms.

In one configuration, the computer circuitry can be further configuredto monitor for TDD UL-DL reconfiguration signals received from the eNBin downlink subframes or special subframes according to a systeminformation block type 1 (SIB1). In addition, the computer circuitry canbe further configured to monitor for TDD UL-DL reconfiguration signalsreceived from the eNB in more than one subframe between two adjacentperiodic instances. Furthermore, a detected TDD UL-DL configuration atthe UE is valid for a window having a duration equal to a definedperiodicity of the TDD UL-DL reconfiguration signal received from theeNB, the defined periodicity including 10 milliseconds (ms), 20 ms, 40ms or 80 ms.

In one example, the UE assumes a same TDD UL-DL configuration for two ormore TDD UL-DL reconfiguration signals received from the eNB when thetwo or more TDD UL-DL reconfiguration signals are detected in subframeswithin a window of a duration equal to a defined periodicity of the TDDUL-DL reconfiguration signals. In addition, the UE includes an antenna,a touch sensitive display screen, a speaker, a microphone, a graphicsprocessor, an application processor, internal memory, or a non-volatilememory port.

Another example provides a method 1100 for performing a Time DivisionDuplex (TDD) uplink-downlink (UL-DL) reconfiguration in a heterogeneousnetwork (HetNet), as shown in the flow chart in FIG. 10. The method maybe executed as instructions on a machine, where the instructions areincluded on at least one computer readable medium or one non-transitorymachine readable storage medium. The method includes the operation ofidentifying cluster metrics for a plurality of nodes in a cell clusterof the HetNet, at a node, wherein the plurality of nodes in the cellcluster have a backhaul latency within a selected range, as in block1110. The method can include selecting a TDD UL-DL configuration indexfor the plurality of nodes in the cell cluster based in part on thecluster metrics, as in block 1120. The method can further includetransmitting the UL-DL configuration index to one or more userequipments (UEs) located within the cell cluster using a downlinkcontrol information (DCI) format, wherein the TDD UL-DL configurationindex is transmitted on a Common Search Space (CSS) of a physicaldownlink control channel (PDCCH) on a UE-specific Primary Cell (PCell),as in block 1130.

In one configuration, the method can further comprise configuringdownlink control information (DCI) monitoring subframes for the one ormore UEs in the cell cluster using radio resource control (RRC)signaling, wherein the one or more UEs monitor for the TDD UL-DLreconfiguration in downlink subframes according to a system informationblock type 1 (SIB1). In addition, the method can further compriseselecting the TDD UL-DL configuration index for the plurality of nodesin the cell cluster based on a minimum, mean or maximum of the clustermetrics, wherein the cluster metrics are exchanged between the pluralityof nodes in the cell cluster over an X2 interface, wherein the clustermetrics include one or more of UL-DL configurations, DL-UL resources,buffer sizes in UL and DL and packet delays.

In one configuration, the method can further comprise transmitting theTDD UL-DL configuration index to the one or more UEs in the cell clusteraccording to an X-bit bitmap indicating a set of system informationblock type 1 (SIB1) downlink or special (DL/S) subframes, wherein theone or more UEs monitor for a downlink channel information (DCI)transmission from the node according to the X-bit bitmap, wherein ‘X’represents a number of bits within a bitmap string in which each bitindicates a particular SIB1 DL/S subframes, wherein a bit “1” indicatesthat the UE shall monitor for a DCI reconfiguration in a correspondingsubframe and a bit “0” indicates that the UE shall not monitor for theDCI reconfiguration in the corresponding subframe. In one example, thenode is selected from a group consisting of a base station (BS), a NodeB (NB), an evolved Node B (eNB), a baseband unit (BBU), a remote radiohead (RRH), a remote radio equipment (RRE), or a remote radio unit(RRU).

FIG. 12 provides an example illustration of the wireless device, such asan user equipment (UE), a mobile station (MS), a mobile wireless device,a mobile communication device, a tablet, a handset, or other type ofwireless device. The wireless device can include one or more antennasconfigured to communicate with a node, macro node, low power node (LPN),or, transmission station, such as a base station (BS), an evolved Node B(eNB), a baseband unit (BBU), a remote radio head (RRH), a remote radioequipment (RRE), a relay station (RS), a radio equipment (RE), or othertype of wireless wide area network (WWAN) access point. The wirelessdevice can be configured to communicate using at least one wirelesscommunication standard including 3GPP LTE, WiMAX, High Speed PacketAccess (HSPA), Bluetooth, and WiFi. The wireless device can communicateusing separate antennas for each wireless communication standard orshared antennas for multiple wireless communication standards. Thewireless device can communicate in a wireless local area network (WLAN),a wireless personal area network (WPAN), and/or a WWAN.

FIG. 12 also provides an illustration of a microphone and one or morespeakers that can be used for audio input and output from the wirelessdevice. The display screen may be a liquid crystal display (LCD) screen,or other type of display screen such as an organic light emitting diode(OLED) display. The display screen can be configured as a touch screen.The touch screen may use capacitive, resistive, or another type of touchscreen technology. An application processor and a graphics processor canbe coupled to internal memory to provide processing and displaycapabilities. A non-volatile memory port can also be used to providedata input/output options to a user. The non-volatile memory port mayalso be used to expand the memory capabilities of the wireless device. Akeyboard may be integrated with the wireless device or wirelesslyconnected to the wireless device to provide additional user input. Avirtual keyboard may also be provided using the touch screen.

Various techniques, or certain aspects or portions thereof, may take theform of program code (i.e., instructions) embodied in tangible media,such as floppy diskettes, CD-ROMs, hard drives, non-transitory computerreadable storage medium, or any other machine-readable storage mediumwherein, when the program code is loaded into and executed by a machine,such as a computer, the machine becomes an apparatus for practicing thevarious techniques. Circuitry can include hardware, firmware, programcode, executable code, computer instructions, and/or software. Anon-transitory computer readable storage medium can be a computerreadable storage medium that does not include signal. In the case ofprogram code execution on programmable computers, the computing devicemay include a processor, a storage medium readable by the processor(including volatile and non-volatile memory and/or storage elements), atleast one input device, and at least one output device. The volatile andnon-volatile memory and/or storage elements may be a RAM, EPROM, flashdrive, optical drive, magnetic hard drive, solid state drive, or othermedium for storing electronic data. The node and wireless device mayalso include a transceiver module, a counter module, a processingmodule, and/or a clock module or timer module. One or more programs thatmay implement or utilize the various techniques described herein may usean application programming interface (API), reusable controls, and thelike. Such programs may be implemented in a high level procedural orobject oriented programming language to communicate with a computersystem. However, the program(s) may be implemented in assembly ormachine language, if desired. In any case, the language may be acompiled or interpreted language, and combined with hardwareimplementations.

It should be understood that many of the functional units described inthis specification have been labeled as modules, in order to moreparticularly emphasize their implementation independence. For example, amodule may be implemented as a hardware circuit comprising custom VLSIcircuits or gate arrays, off-the-shelf semiconductors such as logicchips, transistors, or other discrete components. A module may also beimplemented in programmable hardware devices such as field programmablegate arrays, programmable array logic, programmable logic devices or thelike.

Modules may also be implemented in software for execution by varioustypes of processors. An identified module of executable code may, forinstance, comprise one or more physical or logical blocks of computerinstructions, which may, for instance, be organized as an object,procedure, or function. Nevertheless, the executables of an identifiedmodule need not be physically located together, but may comprisedisparate instructions stored in different locations which, when joinedlogically together, comprise the module and achieve the stated purposefor the module.

Indeed, a module of executable code may be a single instruction, or manyinstructions, and may even be distributed over several different codesegments, among different programs, and across several memory devices.Similarly, operational data may be identified and illustrated hereinwithin modules, and may be embodied in any suitable form and organizedwithin any suitable type of data structure. The operational data may becollected as a single data set, or may be distributed over differentlocations including over different storage devices, and may exist, atleast partially, merely as electronic signals on a system or network.The modules may be passive or active, including agents operable toperform desired functions.

Reference throughout this specification to “an example” means that aparticular feature, structure, or characteristic described in connectionwith the example is included in at least one embodiment of the presentinvention. Thus, appearances of the phrases “in an example” in variousplaces throughout this specification are not necessarily all referringto the same embodiment.

As used herein, a plurality of items, structural elements, compositionalelements, and/or materials may be presented in a common list forconvenience. However, these lists should be construed as though eachmember of the list is individually identified as a separate and uniquemember. Thus, no individual member of such list should be construed as ade facto equivalent of any other member of the same list solely based ontheir presentation in a common group without indications to thecontrary. In addition, various embodiments and example of the presentinvention may be referred to herein along with alternatives for thevarious components thereof. It is understood that such embodiments,examples, and alternatives are not to be construed as defactoequivalents of one another, but are to be considered as separate andautonomous representations of the present invention.

Furthermore, the described features, structures, or characteristics maybe combined in any suitable manner in one or more embodiments. In thefollowing description, numerous specific details are provided, such asexamples of layouts, distances, network examples, etc., to provide athorough understanding of embodiments of the invention. One skilled inthe relevant art will recognize, however, that the invention can bepracticed without one or more of the specific details, or with othermethods, components, layouts, etc. In other instances, well-knownstructures, materials, or operations are not shown or described indetail to avoid obscuring aspects of the invention.

While the forgoing examples are illustrative of the principles of thepresent invention in one or more particular applications, it will beapparent to those of ordinary skill in the art that numerousmodifications in form, usage and details of implementation can be madewithout the exercise of inventive faculty, and without departing fromthe principles and concepts of the invention. Accordingly, it is notintended that the invention be limited, except as by the claims setforth below.

What is claimed is:
 1. An evolved node B (eNB) operable to perform aTime Division Duplex (TDD) uplink-downlink (UL-DL) reconfiguration in aheterogeneous network (HetNet), the eNB having computer circuitryconfigured to: identify cluster metrics for a plurality of evolved nodeBs (eNBs) in a cell cluster of the HetNet, wherein the plurality of eNBsin the cell cluster have a backhaul latency within a selected range;select a TDD UL-DL configuration index for the plurality of eNBs in thecell cluster based in part on the cluster metrics; and transmit the TDDUL-DL configuration index to one or more user equipments (UEs) locatedwithin the cell cluster using a downlink control information (DCI)format, wherein the TDD UL-DL configuration index is transmitted on aCommon Search Space (CSS) of a physical downlink control channel (PDCCH)on a UE-specific Primary Cell (PCell).
 2. The computer circuitry ofclaim 1, further configured to configure downlink control information(DCI) monitoring subframes for the one or more UEs in the cell clusterusing radio resource control (RRC) signaling in a UE-specific manner. 3.The computer circuitry of claim 1, wherein the cluster metrics areexchanged between the plurality of eNBs in the cell cluster over an X2interface, the cluster metrics including one or more of UL-DLconfigurations being used by eNBs within the cell cluster, DL-ULresources required by each eNB, buffer sizes in UL and DL transmissiondirection and packet delays.
 4. The computer circuitry of claim 1,further configured to select the TDD UL-DL configuration index for theplurality of eNBs in the cell cluster based on a minimum, mean ormaximum of the cluster metrics exchanged between the plurality of eNBsin the cell cluster in a distributed manner.
 5. The computer circuitryof claim 1, further configured to select the TDD UL-DL configurationindex for the plurality of eNBs in the cell cluster according to adefined periodicity, wherein the defined periodicity is based on thebackhaul latency of the plurality of eNBs in the cell cluster andincludes 10 milliseconds (ms), 20 ms, 40 ms and 80 ms.
 6. The computercircuitry of claim 1, further configured to use a System Frame Number(SFN) counter to control a radio frame having a SFN mod periodicity ofzero, wherein the TDD UL-DL configuration index is applied by eNBs inthe cell cluster so that the TDD UL-DL configuration is synchronouslyupdated by eNBs within the cell cluster.
 7. The computer circuitry ofclaim 1, further configured to transmit TDD UL-DL configuration indexinformation to the one or more UEs in the cell cluster via a Uuinterface, the TDD UL-DL configuration index information beingtransmitted on a physical downlink control channel (PDCCH) in one ormore of subframe numbers 0, 1, 5 or 6 in each radio frame depending on aUE-specific RRC configuration.
 8. The computer circuitry of claim 1,further configured to transmit the TDD UL-DL configuration index to theone or more UEs in the cell cluster according to a predefinedperiodicity of 10 subframes to 80 subframes and a predefined offsetvalue of 0 subframes to 3 subframes.
 9. The computer circuitry of claim1, further configured to transmit the TDD UL-DL configuration index tothe one or more UEs located in proximity to one or more transmissionpoints (TPs) in a coordinated multi-point (COMP) scenario 4, wherein theTDD UL-DL configuration index is transmitted to the one or more UEsaccording to traffic conditions associated with the one or more TPs. 10.The computer circuitry of claim 1, further configured to transmit theTDD UL-DL configuration index to the one or more UEs located inproximity to one or more transmission points (TPs) in a coordinatedmulti-point (COMP) scenario 4, wherein the TDD UL-DL configuration indexis transmitted to the one or more UEs according to a DL subframespattern used for downlink channel information (DCI) repeatedtransmission monitoring.
 11. The computer circuitry of claim 1, furtherconfigured to transmit the TDD UL-DL configuration index to the one ormore UEs in the cell cluster according to an X-bit bitmap indicating aset of system information block type 1 (SIB1) downlink or special (DL/S)subframes, wherein the one or more UEs monitor for a downlink channelinformation (DCI) transmission from the eNB according to the X-bitbitmap, wherein ‘X’ represents a number of bits within a bitmap stringin which each bit indicates a particular SIB1 DL/S subframes, wherein abit “1” indicates that the UE shall monitor for a DCI reconfiguration ina corresponding subframe and a bit “0” indicates that the UE shall notmonitor for the DCI reconfiguration in the corresponding subframe.
 12. Auser equipment (UE) operable to implement a Time Division Duplex (TDD)uplink-downlink (UL-DL) reconfiguration in a heterogeneous network(HetNet), the UE having computer circuitry configured to: indicate acapability of supporting a TDD UL-DL reconfiguration functionality to anevolved node B (eNB) via UE capability reporting; receive aconfiguration to enable TDD UL-DL reconfiguration at the UE; receive aTDD UL-DL reconfiguration signal from the eNB in a downlink controlinformation (DCI) message; and update a TDD UL-DL configuration of theUE based on the TDD UL-DL reconfiguration signal transmitted on aphysical downlink control channel (PDCCH) in preconfigured downlink orspecial (DL/S) subframes by the eNB.
 13. The computer circuitry of claim12, wherein the configuration to enable the TDD UL-DL reconfiguration atthe UE includes at least one of a UE-specific reconfiguration radionetwork temporary identifier (RNTI), reconfiguration DCI monitoringsubframes configuration information and an indicator index.
 14. Thecomputer circuitry of claim 12, further configured to receive the TDDUL-DL reconfiguration signal from the eNB according to a definedperiodicity of 10 milliseconds (ms), 20 ms, 40 ms or 80 ms.
 15. Thecomputer circuitry of claim 12, further configured to monitor for TDDUL-DL reconfiguration signals received from the eNB in downlinksubframes or special subframes according to a system information blocktype 1 (SIB1).
 16. The computer circuitry of claim 12, furtherconfigured to monitor for TDD UL-DL reconfiguration signals receivedfrom the eNB in more than one subframe between two adjacent periodicinstances.
 17. The computer circuitry of claim 12, wherein a detectedTDD UL-DL configuration at the UE is valid for a window having aduration equal to a defined periodicity of the TDD UL-DL reconfigurationsignal received from the eNB, the defined periodicity including 10milliseconds (ms), 20 ms, 40 ms or 80 ms.
 18. The computer circuitry ofclaim 12, wherein the UE assumes a same TDD UL-DL configuration for twoor more TDD UL-DL reconfiguration signals received from the eNB when thetwo or more TDD UL-DL reconfiguration signals are detected in subframeswithin a window of a duration equal to a defined periodicity of the TDDUL-DL reconfiguration signals.
 19. The computer circuitry of claim 12,wherein the UE includes an antenna, a touch sensitive display screen, aspeaker, a microphone, a graphics processor, an application processor,internal memory, or a non-volatile memory port.
 20. A method forperforming a Time Division Duplex (TDD) uplink-downlink (UL-DL)reconfiguration in a heterogeneous network (HetNet), the methodcomprising: identifying cluster metrics for a plurality of nodes in acell cluster of the HetNet, at a node, wherein the plurality of nodes inthe cell cluster have a backhaul latency within a selected range;selecting a TDD UL-DL configuration index for the plurality of nodes inthe cell cluster based in part on the cluster metrics; and transmittingthe UL-DL configuration index to one or more user equipments (UEs)located within the cell cluster using a downlink control information(DCI) format, wherein the TDD UL-DL configuration index is transmittedon a Common Search Space (CSS) of a physical downlink control channel(PDCCH) on a UE-specific Primary Cell (PCell).
 21. The method of claim20, further comprising configuring downlink control information (DCI)monitoring subframes for the one or more UEs in the cell cluster usingradio resource control (RRC) signaling, wherein the one or more UEsmonitor for the TDD UL-DL reconfiguration in downlink subframesaccording to a system information block type 1 (SIB1).
 22. The method ofclaim 20, further comprising selecting the TDD UL-DL configuration indexfor the plurality of nodes in the cell cluster based on a minimum, meanor maximum of the cluster metrics, wherein the cluster metrics areexchanged between the plurality of nodes in the cell cluster over an X2interface, wherein the cluster metrics include one or more of UL-DLconfigurations, DL-UL resources, buffer sizes in UL and DL and packetdelays.
 23. The method of claim 20, further comprising transmitting theTDD UL-DL configuration index to the one or more UEs in the cell clusteraccording to an X-bit bitmap indicating a set of system informationblock type 1 (SIB1) downlink or special (DL/S) subframes, wherein theone or more UEs monitor for a downlink channel information (DCI)transmission from the node according to the X-bit bitmap, wherein ‘X’represents a number of bits within a bitmap string in which each bitindicates a particular SIB1 DL/S subframes, wherein a bit “1” indicatesthat the UE shall monitor for a DCI reconfiguration in a correspondingsubframe and a bit “0” indicates that the UE shall not monitor for theDCI reconfiguration in the corresponding subframe.
 24. The method ofclaim 20, wherein the node is selected from a group consisting of a basestation (BS), a Node B (NB), an evolved Node B (eNB), a baseband unit(BBU), a remote radio head (RRH), a remote radio equipment (RRE), or aremote radio unit (RRU)